1. Field of the Invention
The present invention relates to a peripheral device in a computer system, and more particularly to an apparatus and method for queuing a command in an optical disk data reproduction system, such as a compact disk-read only memory (CD-ROM) device or a digital versatile disk-read only memory (DVD-ROM) device, for sequentially receiving and performing a command given from a computer.
2. Description of Related Art
A CD-ROM drive is an auxiliary memory device and is used as a peripheral device of a computer. When the computer gives a command to a peripheral device using a task file register, the peripheral device decodes and performs the command. When a user uses a keyboard to input a command to a peripheral device, such as a CD-ROM drive, the computer decodes the command and sends the decoded command to the peripheral device.
There are two methods by which a computer sends a command to a peripheral device. The first method is used when the computer desires to initialize the peripheral device or to obtain performance characteristics of the peripheral device. Here, a command is given to the peripheral device using a task file register. The second method is used when control data is received from or sent to a microcontroller of a peripheral device such as a CD-ROM drive. Here, each command is sent in a packet. These methods are described in "The Specification of ATA Packet Interface for CD-ROMs (SFF-8020i), Revision 2.6 Proposal" published by Small Forms Factor Committee on Jan. 22, 1996, which is herein incorporated by reference in its entirety.
Conventionally, a system including a CD-ROM drive processes a packet command as follows. First, the computer writes a predetermined command, for example, "A0" in hexadecimal (i.e., 1010 0000 in binary) in a task file register. In response, the CD-ROM drive prepares to receive a command sent in a packet of 12 bytes each. Then, the computer sends the packet command to the CD-ROM drive. The CD-ROM drive decodes the 12-byte packet command and executes the command.
In the conventional method for processing packet commands, additional commands from the computer cannot be sent to the CD-ROM drive until the command presently being carried out is completed, degrading the performance of the entire computer system.